Two similar mathematical problems of quadratic function of one variable in junior high school In a football league, there are two matches between every two teams. There are 90 matches in total. How many pairs will take part in the match? 2. To organize a basketball league, the competition system is in the form of a single cycle (one game between each two teams), and 25 games are planned. How many teams should be invited to participate in the competition?

Two similar mathematical problems of quadratic function of one variable in junior high school In a football league, there are two matches between every two teams. There are 90 matches in total. How many pairs will take part in the match? 2. To organize a basketball league, the competition system is in the form of a single cycle (one game between each two teams), and 25 games are planned. How many teams should be invited to participate in the competition?

1. There are 10 teams in the game
Setting: a total of X teams participated in the competition,
Because every two teams have to play twice,
So there are x (x-1) games, that is, X (x-1) = 90
The solution: x = 10 or - 9, and because the team can't have negative numbers, it can only be x = 10
2. There is no answer to this question, because the team doesn't have half of them